Mach 1 is the local speed of sound – about 1,225 km/h at sea level but only 1,062 km/h at airliner cruise altitude, where it is colder. Concorde cruised at Mach 2.04.
How to use the Mach Number Calculator
- Speed v
- Speed of sound from
- Air temperature
- Speed of sound
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the speed and either the air temperature or the speed of sound.
Inputs explained
| Field | What to enter |
|---|---|
| Speed v | Units: km/h, m/s, mph, knots, ft/s |
| Speed of sound from | Choose one: Air temperature, Direct value |
| Air temperature | Units: °C, K, °F |
| Speed of sound | Units: m/s, km/h, mph, ft/s, knots, km/s |
Example values
How the main result changes when Speed v changes and everything else stays at the example values above:
| Speed v (km/h) | Mach number |
|---|---|
| 450 | 0.4236 |
| 675 | 0.6354 |
| 900 | 0.8473 |
| 1,125 | 1.0591 |
| 1,350 | 1.2709 |
| 1,800 | 1.6945 |
Formula
M = v / a, a = √(γ·R·T) (air: γ = 1.4, R = 287.05 J/(kg·K))
Worked example
Inputs — Speed v: 900 km/h; Speed of sound from: Air temperature; Air temperature: -56.5 °C.
Results — Speed of sound = 295.06802 m/s; Mach number = 0.8473; Regime = Transonic.
Key terms
- Mach number
- Speed divided by the local speed of sound.
Frequently asked questions
Why does the speed of sound change with altitude?
It depends on temperature, which falls with height.
What Mach do airliners cruise at?
About 0.78–0.85.
What is hypersonic?
Above about Mach 5.
Does air pressure affect Mach 1?
Not directly – temperature dominates.